Baggage Base size

The rules state the minimum baggage area is 8BU minimum perimeter.So is this square?
For 28mm that would be 9cm x 8cm-72 cm.If not square, how deep would the rectangle be?

The other thing that strikes me is that 18cm frontage for cavalry units is quite lengthy in game terms so this makes them quite unwieldy .I see from the rules book illustrations units that are broken up into what appear to be smaller sizes-2 riders.Any advantage to this apart from mixed horse & musket units?
Thanks

With baggage the depth depends on the frontage, so the more of the perimeter you use on frontage the less remains to use as depth

With cavalry units keep the 18cm frontage at all times. They are a bit unwieldy but the idea is that you take that into account in playing the game